OHM Question for Cabs/Heads

[3k Mylz]

So I have gone through about all I can find from Manufacturers Cut Sheets, and searched the forum for answers, so I am posting what could be a tired post, but here goes:

I want the setup that gives me the most overall headroom, and gives me the truest output for both the cabs and the DI output alike.

I run an Ashdown MAG600, with Ashdown 2X10 and 1X15.

OHM rating out of the head is 4 OHM min, inputs to the cabs are 8 OHM, 300W each. Both Cabs have Parellel Inputs (2). The Head has (2) Mono Outs.

Here's the dilema - I can run the Amp out to the first cab, then parellel to the 2nd, or home run the output of the head to each cab.

Of course, should I home run it, I have an 8 Ohm resistance on the setup. Should I run them in series, I have an OHM change from 8 to 4 - Or so I think. I cant find an Answer on Ashdowns cut sheets for the head. Therefore I dont know if the output is 2X300 W or 600W total output regardless of number of outputs, so if I home run each cab is my output 150W X2. This of course would cut my output wattage in half twice, which would require me to adjust a higher output and may cause the Board to really tun me down, and you know how sound guys are! My entire setup is MOD free.

Anyone out there have experience with this?

 

[David Jayne]

It doesn't matter how you hook them up- it's parallel with either method, and a 4ohm total load. 300 watts to each cab.

 

[René_Julien]

Yup.


You only have one poweramp in the MAG 600. (Not two like in a stereo amp for example.)


So with two cabs you have 575W at your disposal.

With one 8 ohm cab you the amp probably can deliver 300 - 350 W.

You'll never reach that at home practice. 300W is damn loud.

I don't know how big your house is though.



BTW, placing cabs in series (which is not a good idea anyway or not a good idea almost ever) your amp has an 16 ohm load, so will probably put out 150W.


Those two speaker outputs are parallel... they are the same output, only twice (internally directly linked.)

 

[dmrogers]

Generally speaking, amplifier head manufacturers will list the wattage of their amps at specific impedance.

For instance, 750 watts at 4 Ohm load, 400 watts at 8 Ohm load etc....

The speaker cabinets are acting as resistance to the current that the amp is putting out. Running a cab at an impedance (resistance) less than its rated minimum is asking for trouble. By the same token, running it at more impedance (resistance) than the minimum, while not hurting the head, will result in lower power.

Total impedance = 1/(1/a + 1/b + 1/c ... + 1/n)

in your case: Total=1/(1/8+1/8)
or: 1/(1/8+1/8) = 4 Ohms

Talkbass sticky explaining Ohms and impedance

You can read much more about this in the sticky listed above.

So, in your case, your head is putting out maximum wattage with your 4 Ohm load, since your cabs are 8 ohms each.

Of course there are exceptions to my generalized statements that you have to consider. For instance the Genz Benz ShuttleMax 12.0 has two separate power outputs. Each one having a minimum load. You can also rewire cabs and make special cables that changes the overall impedance of cabinets etc......

Hope this helps.

 

[3k Mylz]

Thanks to all, I am glad i can count on TB when Im not certain!